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IMPORTANT: Our store is located in Canada. All orders that include products manufactured outside of Canada or USA will be subject to tariffs and duties, regardless of the order value. US customers are responsible for all applicable duties and tariffs, and those will be billed by the carrier, except for the Lacerta upgrade kit, for which we collect them at checkout.
IMPORTANT: Our store is located in Canada. All orders that include products manufactured outside of Canada or USA will be subject to tariffs and duties, regardless of the order value. US customers are responsible for all applicable duties and tariffs, and those will be billed by the carrier, except for the Lacerta upgrade kit, for which we collect them at checkout.

Correctors and Reducers

Round stars in the corners are not a processing achievement — they are a spacing achievement. Field flatteners and reducers correct the curved focal plane and off-axis aberrations that every telescope has to some degree, and they only work when spaced to within about a millimetre of their design distance. David Astro carries field flatteners and reducers in Canada, shipping from Canadian stock.

This is the category where our back-focus calculation service saves the most frustration. Send us your telescope, camera and filters and we will specify the corrector and the exact spacers to go with it.

Filters

$1,019.80 - $1,019.80
$1,019.80
$1,019.80 - $1,019.80
$1,019.80

Starizona HyperStar V4 for Celestron 8"

STZ-HS4-C8HD-M42-17.5

Focal Ratio: f/2.1 Focal Length: 425mm Compatible Telescopes: Celestron 8" Schmidt-Cassegrain (SCT) & EdgeHD 800 Largest Usable Sensor: 27mm d...

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$1,019.80 - $1,019.80
$1,019.80
$1,019.80 - $1,019.80
$1,019.80
$1,199.00 - $1,328.00
$1,199.00 - $1,328.00
$1,199.00 - $1,328.00
$1,199.00

Starizona HyperStar V4 for Celestron 9.25"

Options available

FeaturesThe HyperStar 9.25 lens converts a standard Celestron 9.25" SCT from f/10 to f/2.2, making the system 25 times faster. That means 25-times...

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$1,199.00 - $1,328.00
$1,199.00 - $1,328.00
$1,199.00 - $1,328.00
$1,199.00
$499.00 - $499.00
$499.00
$499.00 - $499.00
$499.00

Starizona SCT Corrector LF - Large Format Reducer/Coma Corrector

STZ-SCTCORR-LF
1 in stock

Starizona's SCT Corrector has been an incredibly popular focal reducer and coma corrector, giving astrophotographers with standard Schmidt-Cassegra...

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$499.00 - $499.00
$499.00
$499.00 - $499.00
$499.00
$300.00 - $300.00
$300.00
$300.00 - $300.00
$300.00

Starlight Instruments Housing Only w/o SIPS Optics

SI-SIPSHOUSING

Enables use of one SIPS optical unit on multiple telescopes Designed for the Starlight Integrated Paracorr System (SIPS) Maintains precise optical...

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$300.00 - $300.00
$300.00
$300.00 - $300.00
$300.00
$850.00 - $850.00
$850.00
$850.00 - $850.00
$850.00

Starlight Instruments SIPS Coma Corrector

SI-SIPS

Integrates Tele Vue's renowned Paracorr Type 2 coma-correcting optics Functions as a stationary, non-adjustable corrector for maximum rigidity Des...

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$850.00 - $850.00
$850.00
$850.00 - $850.00
$850.00
Svbony 0.5x Focal Reducer 1.25" for Telescope Photography & Observing
$15.19 - $15.19
$15.19
$15.19 - $15.19
$15.19

SVBONY 0.5X Focal Reducer - 1.25"

SV-F9154A
2 in stock

Reduces telescope focal length by a 0.5x factor Fits standard 1.25" eyepieces and accessories Threads on via standard M28.5x0.6 filter threads Ful...

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$15.19 - $15.19
$15.19
$15.19 - $15.19
$15.19
SVBONY SV193 0.8X Focal Reducer / Field Flattener - 2"
SVBONY SV193 0.8X Focal Reducer / Field Flattener - 2"
$83.59 - $83.59
$83.59
$83.59 - $83.59
$83.59

SVBONY SV193 0.8X Focal Reducer / Field Flattener - 2"

SV-W9152D

0.8x Focal Reduction Factor Specifically designed for the SVBONY SV503 102ED Telescope Corrects for field curvature for flat, sharp stars 3-Elemen...

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$83.59 - $83.59
$83.59
$83.59 - $83.59
$83.59
Svbony SV199 1.25" ADC Atmospheric Dispersion Corrector
$79.64 - $79.64
$79.64
$79.64 - $79.64
$79.64

SVBONY SV199 ADC Atmospheric Dispersion Corrector - 1.25"

SV-W9157B

Corrects atmospheric dispersion for planetary viewing 2° to 2.5° prism deviation angle 24mm clear optical aperture Fits standard 1.25" focusers an...

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$79.64 - $79.64
$79.64
$79.64 - $79.64
$79.64
SVBONY SV209 1.0X Field Flattener for SV550 80F6
SVBONY SV209 1.0X Field Flattener for SV550 80F6
$119.99 - $119.99
$119.99
$119.99 - $119.99
$119.99

SVBONY SV209 1.0X Field Flattener for SV550 80F6

SV-W9161A

1.0x focal correction factor Designed for the Svbony SV550 80F6 telescope 45mm fully illuminated image circle M63x1 telescope-side connection Prov...

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$119.99 - $119.99
$119.99
$119.99 - $119.99
$119.99
Tele Vue 0.8x Focal Reducer 1
$403.00 - $403.00
$403.00
$403.00 - $403.00
$403.00

Tele Vue 0.8x Focal Reducer

TV-TRF-2008

Reduction Factor: 0.8x Optical Design: Reducer and Field Flattener Telescope Connection: 2-inch Barrel Camera Connection: M42x0.75 T-Ring Thread O...

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$403.00 - $403.00
$403.00
$403.00 - $403.00
$403.00
Tele Vue 0.8x Reducer for NP Scopes 2
Tele Vue 0.8x Reducer for NP Scopes 1
$572.00 - $572.00
$572.00
$572.00 - $572.00
$572.00

Tele Vue 0.8x Reducer for NP Scopes

TV-NPR-2073

Focal Length Reduction Factor: 0.8x Optical Design: 4-element, 3-group Telescope Interface: 2.4" Slip-fit Barrel Camera Interface: Threaded for Te...

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$572.00 - $572.00
$572.00
$572.00 - $572.00
$572.00
Tele Vue 0.8x Reducer-Flattener for 102 Scopes 2
Tele Vue 0.8x Reducer-Flattener for 102 Scopes 1
$446.00 - $446.00
$446.00
$446.00 - $446.00
$446.00

Tele Vue 0.8x Reducer-Flattener for 102 Scopes

TV-RFL-4087

Reduction Factor: 0.8x Effective Focal Length (on TV-102): 704mm Effective Focal Ratio (on TV-102): f/6.9 Compatibility: TV-102 and 800-1000mm f...

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$446.00 - $446.00
$446.00
$446.00 - $446.00
$446.00
Tele Vue Big Paracorr Type 2 2
Tele Vue Big Paracorr Type 2 1
$1,253.00 - $1,253.00
$1,253.00
$1,253.00 - $1,253.00
$1,253.00

Tele Vue Big Paracorr Type 2

TV-VIP-3010

Corrects Coma in Newtonian Reflectors For f/3 to f/6 Parabolic Mirrors 1.15x Magnification Factor Designed for 3-inch Focusers Prevents Vignetting...

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$1,253.00 - $1,253.00
$1,253.00
$1,253.00 - $1,253.00
$1,253.00
Tele Vue Large Field Corrector- NP101-NP101is-NP127is 2
Tele Vue Large Field Corrector- NP101-NP101is-NP127is 1
$343.00 - $343.00
$343.00
$343.00 - $343.00
$343.00

Tele Vue Large Field Corrector- NP101-NP101is-NP127is

TV-LCL-1069

Corrects Field Curvature for Large Format Sensors Designed for Tele Vue NP101, NP101is, and NP127is Telescopes Fully Illuminates Sensors up to 52m...

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$343.00 - $343.00
$343.00
$343.00 - $343.00
$343.00
Tele Vue Paracorr Type 2 2
Tele Vue Paracorr Type 2 1
$577.00 - $577.00
$577.00
$577.00 - $577.00
$577.00

Tele Vue Paracorr Type 2

TV-VIP-2010
1 in stock

Corrects Coma in Fast Newtonian Reflectors For f-ratios as fast as f/3 1.15x Magnification Factor Adjustable "Tunable Top" for Eyepiece Optimizati...

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$577.00 - $577.00
$577.00
$577.00 - $577.00
$577.00
$278.00 - $278.00
$278.00
$278.00 - $278.00
$278.00

William Optics Adjustable Flat61 for Z61

WO-P-FLAT61A
1 in stock

1.0x Flattener Power Designed for William Optics Zenithstar 61 Full-Frame Sensor Coverage Adjustable Back Focus Mechanism M54 Telescope Thread &am...

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$278.00 - $278.00
$278.00
$278.00 - $278.00
$278.00
$269.00 - $269.00
$269.00
$269.00 - $269.00
$269.00

William Optics Adjustable Flat6AIII

WO-P-FLAT6AIII
2 in stock

0.8x Focal Reducer & Field Flattener Optimized for GT71, GT81, Z81 & Z103 Refractors Illuminates Full-Frame Sensors Adjustable Back Focus ...

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$269.00 - $269.00
$269.00
$269.00 - $269.00
$269.00
$348.00 - $348.00
$348.00
$348.00 - $348.00
$348.00

William Optics Adjustable Flat6AIII for FLT91

WO-P-FLAT6AIII-M92

Dedicated Field Flattener for the William Optics FLT91 Telescope Corrects Field Curvature for Pinpoint Stars Edge-to-Edge Integrated Adjustment Ri...

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$348.00 - $348.00
$348.00
$348.00 - $348.00
$348.00
$278.00 - $278.00
$278.00
$278.00 - $278.00
$278.00

William Optics Adjustable Flat73A for Z73

WO-P-FLAT73A
1 in stock

Designed specifically for the William Optics ZenithStar 73 APO Delivers a 1.0x, perfectly flat field across full-frame sensors Connects to the Z73...

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$278.00 - $278.00
$278.00
$278.00 - $278.00
$278.00
$284.00 - $284.00
$284.00
$284.00 - $284.00
$284.00

William Optics Adjustable Reducer Flattener Flat61R for Z61

WO-P-FLAT61R

Adjustable reducer and field flattener for William Optics Z61 telescope Improves image sharpness and reduces distortion Description ...

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$284.00 - $284.00
$284.00
$284.00 - $284.00
$284.00
$284.00 - $284.00
$284.00
$284.00 - $284.00
$284.00

William Optics Adjustable Reducer Flattener Flat73R for Z73

WO-P-FLAT73R

Reduces focal length by a factor of 0.8x Designed for the William Optics Zenithstar 73 telescope Provides edge-to-edge flat field for full-frame s...

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$284.00 - $284.00
$284.00
$284.00 - $284.00
$284.00
$788.00 - $788.00
$788.00
$788.00 - $788.00
$788.00

William Optics Flattener 68III

WO-P-FLAT68III

1.0x Flattener Power preserves native focal length Corrects field curvature for Full Frame sensors Designed for William Optics FLT132, GT102, and ...

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$788.00 - $788.00
$788.00
$788.00 - $788.00
$788.00
William Optics Ultra Flat 132 (0.79x Reducer)
$1,068.00 - $1,068.00
$1,068.00
$1,068.00 - $1,068.00
$1,068.00

William Optics Ultra Flat 132 (0.79x Reducer)

WO-P-FLAT-132

Reduces focal ratio by a factor of 0.79x Provides a flat field for Full Frame, APS-C, and M4/3 sensors 3-element, 3-group optical design Connects ...

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$1,068.00 - $1,068.00
$1,068.00
$1,068.00 - $1,068.00
$1,068.00
William Optics Ultra Flat 156 (0.79x Reducer)
$1,068.00 - $1,068.00
$1,068.00
$1,068.00 - $1,068.00
$1,068.00

William Optics Ultra Flat 156 (0.79x Reducer)

WO-P-FLAT-156

Reduces focal ratio by a factor of 0.79x Designed for Medium Format, Full Frame, and APS-C sensors 3-element, 3-group optical design Requires 75.5...

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$1,068.00 - $1,068.00
$1,068.00
$1,068.00 - $1,068.00
$1,068.00

Flatteners, Reducers and Coma Correctors

Each type solves a different optical problem, and using the wrong one degrades the field instead of correcting it.

  • Field flatteners: Correct focal plane curvature without changing focal length, so framing stays the same and only corner star shape improves.
  • Focal reducers: Flatten and shorten focal length, typically to 0.8x or 0.7x, widening the field and increasing the effective focal ratio for shorter exposures.
  • Coma correctors: For Newtonian reflectors, correcting the comet-shaped off-axis stars inherent to a parabolic mirror, essential below about f/6.
  • SCT reducer-correctors: Typically 0.63x units for Schmidt-Cassegrains, which both widen the field and considerably reduce exposure times at long focal lengths.
  • Telescope-specific versus universal: A corrector designed for your exact tube will outperform a universal one, particularly at the corners of large sensors.
  • Back-focus specification: Every corrector has a design distance from its rear surface to the sensor, commonly 55 mm. Missing it produces elongated corner stars pointing either inward or outward.

Why Choose David Astro for Field Flatteners and Reducers

A corrector is one of the few products where the accessory list matters as much as the product itself.

  • Back-focus calculated and spacers supplied: We provide the full component list including fine shims, and account for the focal shift your filter glass introduces.
  • Star shape diagnosis: If your corners are wrong, the direction of elongation tells us whether you are over- or under-spaced. Send us a corner crop and we will tell you which way to move.
  • Telescope-matched selection: We identify the corrector designed for your specific tube rather than defaulting to a universal unit that will underperform on a large sensor.
  • Authorized dealer: Genuine correctors with full manufacturer warranty, held in stock for fast domestic shipping.
  • Ships from Canada: No duties or brokerage fees for Canadian customers.

Field Flatteners and Reducers in Canada — Frequently Asked Questions

How precise does back-focus have to be?
Within about one millimetre for most correctors, and tighter at fast focal ratios. That is why filter thickness matters — a 3 mm filter shifts focus by roughly 1 mm, which is the entire tolerance.
My corner stars are elongated. Am I over or under spaced?
Stars elongated radially, pointing away from centre, generally indicate too much spacing. Tangentially elongated stars generally indicate too little. Send us a corner crop and we will confirm and give you a number.
Flattener or reducer?
Use a flattener if your framing is already right and only the corners are wrong. Use a reducer if you also want a wider field and shorter exposures, accepting that your image scale drops.
Will a universal corrector work on my telescope?
Sometimes acceptably, but a corrector matched to your specific tube will correct better at the edges, especially with an APS-C or larger sensor. Tell us your tube and we will check what exists for it.

Chasing corner stars?

Send us your imaging train and a corner crop. We will calculate the spacing and specify the parts. Held in Canada, shipped fast.